As you are accumulating supplies it's good to have a bit of balance.
I like to try and keep my powder and primers somewhat balanced. For example, 8lbs of W231 gives me just over 10,000 .45 loads (10,181 at 5.5gr).
It makes more sense (to me anyway) to get 2 cases (5k/case) of primers for each 8lb powder instead of stocking up on just powder.